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Thirsty astronauts orbiting the Earth aboard the International Space Station (ISS) have just gained a handy new source of water to eke out supplies shipped up from Earth and those from the station's famously erratic urine recycling system.

The new Sabatier Reactor, named for the Nobel prize-winning French chemist who developed the process it uses, will combine hydrogen and carbon dioxide to produce water and methane.

The station's life support machinery generates oxygen to keep the crew alive by splitting water. Astronauts breathe the oxygen and emit CO2, which is removed from the internal atmosphere by scrubber machinery and - at the moment - thrown away.

The hydrogen from the oxygen generators is currently also dumped into space as waste, but will now be combined with CO2 from the scrubbers to reclaim useful water. According to Hamilton Sundstrand Space Land & Sea, makers of the reactor, it should produce almost a tonne of water every year. The reactor was delivered to the station by space shuttle Discovery, which will undock for return to Earth tomorrow.

In addition to oxygen generation, the ISS also needs water for drinking, washing, cooking and cooling some electronic equipment. Historically about half the station's requirements were met by recycling used water, and the rest by deliveries from visiting space shuttles. The shuttles didn't normally need to use up payload space for this, as their fuel-cell electric generators produce clean water as an exhaust product.

With the recent doubling of the ISS crew to six people and the imminent disappearance of the shuttles, the station needs to recycle as much water as it possibly can so as to save payload space on flights up from Earth. A trouble-plagued $250m barrel-shaped centrifugal Urine Processor Assembly has been installed to purify astronauts' and cosmonauts' personal wastes, in addition to existing kit which processed airborne sweat and domestic "grey water".

Now the Sabatier Reactor is ready to start doing its bit. The machine was supplied by Hamilton Sundstrand under a novel contract based on the amount of water it actually produces. Announcing the deal two years ago, NASA spokesmen stated:

NASA will not buy hardware, but instead will purchase the water service. If the system does not work, NASA will not pay for it.

If the reactor works, Hamilton Sundstrand could receive up to $65m by 2014.

The potential exists to refine the process further and break the Sabatier reactor's methane exhaust into carbon and hydrogen. In that case the hydrogen would be reclaimed - perhaps for use as a fuel, or for feeding back into the water loop by combination with surplus oxygen or CO2 as might suit. The only waste product then would be carbon (originating from the astronauts' food supplies) deposited in the reactor as graphite. ®